The present invention relates to computer animation. More specifically, the present invention relates to methods and apparatus for filtering of illumination effects for computer animation.
Throughout the years, movie makers have often tried to tell stories involving make-believe creatures, far away places, and fantastic things. To do so, they have often relied on animation techniques to bring the make-believe to “life.” Two of the major paths in animation have traditionally included, drawing-based animation techniques and stop motion animation techniques.
Drawing-based animation techniques were refined in the twentieth century, by movie makers such as Walt Disney and used in movies such as “Snow White and the Seven Dwarfs” (1937) and “Fantasia” (1940). This animation technique typically required artists to hand-draw (or paint) animated images onto a transparent media or cells. After painting, each cell would then be captured or recorded onto film as one or more frames in a movie.
Stop motion-based animation techniques typically required the construction of miniature sets, props, and characters. The filmmakers would construct the sets, add props, and position the miniature characters in a pose. After the animator was happy with how everything was arranged, one or more frames of film would be taken of that specific arrangement. Stop motion animation techniques were developed by movie makers such as Willis O'Brien for movies such as “King Kong” (1933). Subsequently, these techniques were refined by animators such as Ray Harryhausen for movies including “Mighty Joe Young” (1948) and Clash Of The Titans (1981).
With the wide-spread availability of computers in the later part of the twentieth century, animators began to rely upon computers to assist in the animation process. This included using computers to facilitate drawing-based animation, for example, by painting images, by generating in-between images (“tweening”), and the like. This also included using computers to augment stop motion animation techniques. For example, physical models could be represented by virtual models in computer memory, and manipulated.
One of the pioneering companies in the computer-aided animation (CA) industry was Pixar. Pixar is more widely known as Pixar Animation Studios, the creators of animated features such as “Toy Story” (1995) and “Toy Story 2” (1999), “A Bugs Life” (1998), “Monsters, Inc.” (2001), “Finding Nemo” (2003), “The Incredibles” (2004), and others. In addition to creating animated features, Pixar developed computing platforms specially designed for CA, and CA software now known as RenderMan®. RenderMan® was particularly well received in the animation industry and recognized with two Academy Awards®. The RenderMan® software included a “rendering engine” that “rendered” or converted geometric and/or mathematical descriptions of objects into intermediate rendering data and/or into two dimensional image representations.
One of the most accurate and straightforward approaches to determining global illumination (including direct and non-direct illumination) for rendering scenes in computer graphics is with ray tracing. In this method, a rendering engine casts a large number of rays from either light sources or surface points, or both, for the purpose of evaluating light transport paths and connectivity, including diffuse bounces, between surface points and the lights.
One drawback with current ray tracing techniques is that it is necessary to cast a large number of rays in order to produce an accurate value for the path integral. For animated features this is an especially severe limitation because of the time-consuming nature of ray tracing. With the large number of images that are rendered in a feature animation, the total number of ray tracing operations is prohibitively high.
A drawback noted by the inventors is that the casting of rays is different for different rendered images. Accordingly, for rendered images that are played-back to a user, unacceptable flickering or buzzing artifacts may appear because of the different sample points between frames. Such artifacts may make surfaces appear as a sparkling, flickering, or animated when such surfaces are supposed to be uniform in appearance.
One technique that may be used to address these drawback is to greatly increase the number of stochastic rays cast for each image to be rendered. In some known examples, the number of rays cast per pixel may be on the order of 500 to 1000. This solution, however is very time consuming and dramatically increases the total rendering time.
FIGS. 2A-E illustrates a series of screen sequences in which non-direct illumination changes versus time. More specifically, FIGS. 2A-E illustrates low-sampling-resolution ray-traced rendered images of a three dimensional scene having fixed geometric elements where an illumination source moves circularly in space with respect to time. In this example, the number of rays cast per pixel is relatively low, e.g. 16 rays /pixel, thus as can be seen in FIGS. 2A-E, the resulting images 200-240 have significant noise and noise-related artifacts. For example, as seen in images 200-220, the portions 310, 320, 325 representing the floor of the box appears very grainy or textured, although the floor of the box should appear smooth or not-textured. Additionally, carefully comparing images 200-220 the apparent texture of the floor is not the same between the images. To a user who views images 200-220 successively, as in an animation, the floor of the box will appear to “sparkle” or “hiss.”
Another type of noise-related artifact is seen in images 230 and 240. In image 230, the portion 330 representing the back wall has a discernable pattern 340; and in image 240, the portion 345 representing the back wall also has a discernable pattern 350. These patterns are typically different. Discernable patterns 330 and 340 are distracting artifacts within images 230 and 240. Additionally, as a discussed above, when image 230 and 240 are successively displayed to a user, for example in the form of an animation, discernable patterns 330 and 340 make the back wall appear to “creep” or fluctuate, although the back wall should be stationary. Such patterns are often a result of assumptions made during a rendering operation, and are often dependent upon the rendering engine used.
Another technique used to address these drawbacks is by post-processing of the rendered image with a low-pass filter. A drawback to such processes is that fine geometric features of an object, such as corners, creases, hair, etc, will be blurred in the rendered image. As a result, the blurred rendered image will appear dull and will not appear as sharp or crisp to the audience.
Accordingly, what is desired are improved methods and apparatus for improved rendered images without the drawbacks discussed above.